Protagoras

Protagoras (490 BC-420 BC) was a Presocratic philosopher and sophist from Thrace. He invented the role of professional sophist, and he created a controversy in his time by proclaiming that "Man is the measure of all things," interpreted by Plato to mean that there is no absolute truth.

Biography
Protagoras was born in Abdera, Thrace in 490 BC, and he worked as a porter, using perfect geometric accuracy to tie together small pieces of wood with a cord. The philosopher Democritus noticed this, and he was impressed by Protagoras' mathematical skills. He took him into his own household and taught him philosophy, and Protagoras became well-known in Athens and even a friend of Pericles. Around 450 BC, he became a sophist, and he invented professional sophism, teaching excellence and virtue to young statesmen and nobility. He believed that, on any matter, there were two arguments opposed to one another, and he invented the concept of relativism. His argument that "Man is the measure of all things" also meant that there is no absolute truth, but which individuals deem to be the truth. Protagoras supported the idea of agnosticism in his work On the Gods, leading to the Athenians expelling him from the city and burning his books. He later returned to Athens, and, in 431 BC, at Pericles' symposium, Protagoras had a debate with Hermippus about the populist politician Cleon, whom Hermippus saw as a champion of the people, while Protagoras saw him as a brute (which the mercenary Kassandra, who entered the conversation, agreed with). He died in 420 BC.